differenceblog, posts by tag: vision - LiveJournal

Fairfield and Fletcher's 2002 review of vitamin benefits and risks states that vitamin A is critical for night vision, but in doses as small as 3x the RDA, can cause birth defects. Katz et al (1995) found that night blindness was prevalent among lactating and pregnant Nepalese women, which they attributed to vitamin A deficiency, although Wedner et al (2004) did not find that self-reported night blindness was a good predictor of vitamin A deficiency in a Tanzanian population. Taren et al (2004) suggest that the "Night Vision Threshold Test" is a more accurate predictor, and finds nearly three times as many cases of reduced night vision as self-report.

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In October ("I can see clearly"), I mentioned Carlson's review of Taking Sex Differences Seriously (Rhoads, 2004), which apparently claims that women have better night vision. I still haven't managed to find any citation for this claim. While I've certainly encountered more women than men who complain of reduced night vision, I suspect this is more reporting bias than actual fact, a suspicion backed up by Brabyn et al's (2005) finding that women (even with better vision) are more likely to voluntarily restrict themselves to daytime driving than men.

edit: "Deviantart News" article (3/17/07) found by huGoFdeStruction "somewhere in the net" claims that "women have more cones and men have more rods". An April 4th comment by "Neuropsychguy" suggests that this is a misinterpretation of tetrachromacy data.

Jiang et al (2006) tested the effect of "invisible" erotic pictures on the attention of gay/bisexual and heterosexual males and females. After comparing attraction/repulsion to male or female erotic stumuli, Jiang et al found that while gay men responded like heterosexual women to the suppressed images, gay/bisexual women responded in between this group and the heterosexual men. Lykins et al (2006) found that both men and women focused less on faces and more on bodies in response to normally presented erotic (vs. non-erotic) stimuli, and the results suggested that women's attentional patterns may be more affected than men's by the erotica context. However, Lykins et al point out that because their study showed different pictures to the male and female groups (heterosexually delineated) comparison between groups is not valid.

Neither of these studies report the menstrual cycle stage of female participants, which may be an issue. Gizewski et al (2006) studied fMRI results of 25 women during mid-luteal phase (post ovulation) and during menses. Self-reported arousal in women was similar to men's at the mid-luteal test, but significantly lower at menses. Some activation differences between mid-luteal and menstrual phases were reported (e.g. reduced in the left thalamus at menses). However, between-sex differences were more robust than menstrual phase differences.

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One big concern I have with studies using "erotic stimuli" is the source of the images. Lykins et al wrote that they got their images of females from Playboy's website, and images of males from Falcon Studio's website. Both of these websites design their erotic content for men. Unfortunately, I can't think of any source for erotic images of men by women that would match Playboy on production values. Obviously, more women-driven erotica needs to be produced, in the name of science!

In humans, color blindness is much more common in males than females (7% vs. 0.4%, according to Montgomery, 1997). Jordan and Mallon (1993) suggest that there may be some women who are tetrachromats: they may see in four wavelengths, instead of the three that most humans get. Color vision is dependent on cone cells in the eye, and the expression of cone cells seems to be programmed on the X-chromosome. Glenn Zorpette's 2000 article "Searching for Madam Tetrachromat" goes further into why tetrachromacy is only expected in women.

An extra color channel in females is hardly unheard of. Gerald Jacobs (2004) found that most squirrel monkeys are dichromats (2 colors). The only squirrel monkeys that were trichromats (3 colors) were some of the females. Mark Prescott (2006) suggests that this is evolutionarily related to the brightly colored markings on some male new world monkeys -- the females can distinguish them, but their male competitors can not.

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I think everyone can find something to be excited about in tetrachromacy. My partner suggested titling today's piece "D00d! Chicks be stealin' yer conez!" and then started babbling about how great a "hidden roles" game you could make out of color blindness. What I find interesting about it is the fact that most of what women tell me that they're better than men at is perception -- they see more. Tetrachromacy, however rare, may be a case where this is literally true.

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Gender differences are often thought to be largely the result of socialization. Many researchers use infant studies as a way to avoid the complications of socialization effect. Connellan et al (2000) found that newborns males would spend more time looking at a mobile whereas female newborns would spend more time looking at a face. This study was coauthored by Simon Baron-Cohen, best known for his "extreme male brain" theory of autism (or possibly for his famous cousin, Sacha Baron Cohen). Leeb and Rejskind (2000) were not able to find gender differences in face gazing in infants under 5 days old, but did find differences in infants at 13-18 weeks. Whether this is a socialization effect or a developmental effect is unclear. Tronick and Cohn (1989) suggest a developmental rate difference between boys and girls in their ability to synchronize with adults, but Culp (1983) demonstrated that adults react very differently to infants based on their perceived gender.

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I have no strong feelings either way about the gender socialization of infants. I am constantly baffled by the wide variety of clothing available for infants (and the often extreme gender specificity of the outfits) but I can't draw any conclusions about how people respond to infants. However, interpreting infant reactions seems to me to be as fuzzy a science as interpreting animal reactions; perhaps more, because the animal's brains are more often at their fully developed stage.

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Humans make judgements about the perceived gender of other humans so quickly that we are usually not aware of having done it. What factors influence these snap decisions? Ganel et al (2002) suggest that identity and gender are inseparably linked in cognitive facial recognition. This is in contrast to other models that suggest identity and sex are processed in separate pathways; Ganel et al only found these routes separable when gender decisions were based on hairstyle. Kovacs et al (2004) found that exposing male raters to gender-specific steroid scents influenced their gender judgment. Hoss et al (2005) found that attractiveness increased speed and accuracy of both male and female classification of faces by adults. Masculinity facilitated classification of males by both adults and children, but facial femininity did not affect identification of females.

A lack of clarity in this decision may be distinctly unsettling. Krendl et al (2006) found (via fMRI) that amygdala activation was stronger in evaluating transsexual and "unattractive" faces than in evaluating pierced, overweight, or control faces. Baudouin and Gallay (2006) found that raters responded to composite faces of males or females as more "distinctive" than composite faces that were not specifically gendered.

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When I was first transitioning, I tried to stop classifying people by gender. This proved to be a lot more difficult than I expected. All I succeeded in doing was being wrong more often, which was enlightening in and of itself. Still, it's upsetting when you realize that the "lesbian" you've been checking out really is a teenaged boy. The only success I've managed on this front is in being less unsettled when I turn out to be wrong. Since I'm very bad at admitting when I'm wrong in other areas of my life, I consider this a major victory.

Krause et al. (1982) surveyed vision correction in 14 year olds in Finland. They found that girls were more likely than boys to have corrective lenses, but that when boys did need correction, their cases of myopia or hyperopia were more pronounced. This suggests that the boys (or perhaps their parents) had a higher threshold for correction-seeking than the girls, which is in line with what we already know about the medical habits of males (see "Playing Doctor", Aug 31). Taylor et al (1997) found higher rates of vision correction in adult women as well. However, Kleinstein's 1984 review calls the vision difference between males and females "small and not well-documented."

In his argument for a return to traditional sex roles, Taking Sex Differences Seriously, Steven E. Rhodes claims that women have better night vision than men, ostensibly to better care for "teary infants in the moonless grass," whereas men have better day vision for hunting (according to a 2004 review by Carlson of the "Family Research Council"). The "Search Your Love" dating advice suggests that women have better peripheral vision than men to help them "to see what’s happening around the house, to spot an approaching danger, to notice changes in the children’s behavior and appearance". However, I was unable to find any backup for either of these assertions.

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I remember desperately wanting glasses in elementary school. In 2nd or 3rd grade, the other kids started to get glasses, and while I remember it was the kids that I wanted to be like who were getting them, the only specific kid I can remember is a boy named Patrick, who had gold aviator frames. I can't remember ever thinking that glasses were uncool or a sign of infirmity, but later I remember thinking that being allowed to wear contacts was a major rite of passage into adulthood. I wore contacts for most of my adolescent and young adult life, but switched back to glasses when I transitioned because having masculine frames helped me "pass" better.